1. Field of the Invention
The present invention relates to an electronically operable access control system, more particularly an electronically controlled access control system utilizing an integrated circuit card or "smart card" as a key to gain access to an access controlled area such as hotel rooms.
2. Description of the Prior Art
The advantages of electronic cards to activate locks and other barrier mechanisms are well known. Instead of changing mechanical tumblers and cutting new metallic keys, lock and key can be programmed and reprogrammed using a computer and software. Moreover, they permit controlled access according to various levels of security.
For example, U.S. Pat. No. Re. 29,259 describes a coding scheme that uses a key field and an authorization field in the key. The key is made of a flat plastic card and the data is encoded on the card via punched holes. If the key field in the key and lock match, the opening mechanism is activated. If the key fields do not match, but the authorization field in the key matches the key field in the lock, the opening mechanism is activated, and the key field in the lock is replaced to match the key field in the card. This prevents a previous guest from using his or her card to enter the room once a new guest has activated the lock.
U.S. Pat. No. 4,717,816 describes an electronic lock and key system that uses a metallic card as a key which carries magnetically-coded data that, when inserted in a slot in the lock, opens the door if coded data in the lock matches either of two codes in the card, the new guest's code or that of the previous guest. Data in the lock can be changed using a portable computer.
However, prior art electronic lock and key systems require a special, single-purpose card for use with a particular lock or sets of locks. Further, the amount of information which can be provided or encoded in the key is limited because of the inherent limitation of encoding associated with punched holes or magnetic strips on the card. For example, the number of levels of security, which can be encoded in the key, is severely limited. Furthermore, prior art lock and key systems do not provide data transfer from the lock to the key. In other words, information encoded in the key can not be directly updated or erased by the lock. Therefore, to deactivate the key, for example, the key has to be brought to a separate system management system. Moreover, information, for example, of transactional or diagnostic nature which is provided from the lock cannot be written into the key directly therefrom. Though an improvement over mechanical lock-and-key units, cards that rely on punched holes or magnetic media provide only limited capabilities.